The field of the present invention is vibratory screening devices and self-cleaning systems therefor.
Vibratory screen separators are well known. Tensioned metal screen cloth is normally used in such devices. Such separators typically employ either rectangular or circular screens which are driven by rotating eccentric weights or other vibration inducing mechanisms. The vibration assists in the passage of material through the screen and in prolonging the effectiveness of the screen. However, blinding of the screen cloth remains a frequent problem.
To substantially prolong the effectiveness of a screen by reducing blinding, self-cleaning systems have been developed. In circular vibratory screening devices, screen assemblies have included self-cleaning systems having a flow-through support surface spanning across the screen frame and located below and substantially parallel to the screen cloth. Such flow-through support surfaces have been defined by perforated metal plates, screens and the like. Normally the support includes openings which are larger than the openings in the overlaying screen cloth. However, other arrangements may be employed in specific circumstances. Sliders are positioned in the space between the support surface and the screen cloth. These sliders are frequently cylindrical in cross section. They are induced by the vibration of the screening mechanism to move about such a circular screening device and impact against the screen cloth under the influence of the vibratory motion of the separator. This repeated impact of the sliders acts to free the screen cloth of material such that it eventually will pass through the screen or be separated off.
With rectangular vibratory screen separator devices, sliders and other self-cleaning elements have not proven as effective. In rectangular systems, either the vibratory motion or screen orientation or both frequently act to concentrate the sliders at one end or corner of the screen. For example, rectangular screens are often placed on an angle; and under such circumstances, the sliders have a tendency to collect at the lower end of the frame. Even with rectangular, level screens, the sliders do not migrate about the screen as well as with a circular screen. Sliders may even migrate uphill under certain vibratory conditions.
Systems have been developed to cause impacting against the screen cloth in rectangular systems. A support surface is used with resilient balls positioned between the screen cloth and the support surface. Angled surfaces are also included as part of the support surface which direct the bouncing balls against the screen cloth. Rectangular screens are frequently operated at an incline and the balls continually return to the angled surface located at the lower end of the frame to be redirected toward the screen cloth.